Axial mode conventional helical antennas (HAs) have been widely used in satellite communications and global positioning systems due to their high gain and circular polarization (CP). The properties of conventional helical antennas have been extensively studied. Segmented helical antennas (SHAs), such as square cross section helical antennas, have been investigated [1]-[3]. The SHAs can provide approximately equivalent performance compared to the conventional helical antenna. The linear segments, which make up an SHA can be easily supported on a dielectric structure. This kind of structure can be designed and manufactured at a very low cost. In addition, the traditional helical antenna only has one sense: either right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP), which is decided by its rolling direction. Thus, CP sense switchable antennas have been developed [18], [17]. However, these antennas need extra switching circuits and power supply. Also, the gain (6 dBi) of existing CP switchable antennas is lower than that of a traditional helical antenna [21].